제일

Etymology 1
.

Adverb

 * 1) most, -est;

Noun

 * 1) number one; the first or primary

Usage notes
The most common use of this is in front of an adjective or adjectival phrase, to denote superlativity.

A 2007 decision by the Patent Court of Korea found that while the superlative sense of is not distinctive, the use of  in front of a noun is distinctive and can be protected by trademark. 

Etymology 2
.

Noun

 * 1) a celebratory or memorial day

Etymology 3
, literally "the day that ends [the year]".

Noun

 * 1) the last day of the lunar year; Lunar New Year's Eve